The invention concerns underwater video lighting, and particularly a unit producing a powerful beam from LED sources, with the ability to adjust light filtration by rotation of a front filter ring. The underwater light may produce flood light at about 4000 lumens and weighs less than two pounds.
A number of underwater lighting devices are available for divers, some with rechargeable batteries and some also including flip-down color filters, such as red filters.
When an underwater photographer, including a video photographer, dives below about thirty feet during daylight, virtually all red has been filtered out of the ambient light. Because of the color adjustment (white balance) that is usually made by the diver's video camera, the colors in the video images will be adjusted to replace the red, but light projected from a diving light will compete with ambient light and areas of the video image that include the artificial light will appear overly red when color-balanced by the camera. The situation is different in night diving, in which the only light available is that from the diving light, and unbalance of color in different areas of the image is not a problem.
Most diving lights previous to this invention have been little more than waterproof flashlights. None has included any filter to address the color balance problem noted above, nor has any included a convenient multi-filter manual selection on a powerful video diving light as in the current invention described below.
The diving light of the invention, particularly for video support, is a relatively large underwater device, yet light in weight, with a beam which can be about 4000 lumens of flood light. Within the light's casing is a battery providing for about one hour of light at 4000 lumens (or about two hours of light at 2000 lumens, or about four hours of light at 1000 lumens).
The dive light of the invention has a snap-on front filter ring, interchangeable with other filter rings as selected, the filter ring being rotatable about the face of the light casing and having several selectable filters. Light projection is from an off-center position on the face of the housing, enabling different filters to be placed in front of the light beam by rotation of the bezel. One important filter preferably included on the dive light is a blue/green filter, which can be used to approximately match the projected light beam to the ambient lighting when diving in conditions of near-total red depletion from the natural light.
The light source of the device is a very tight cluster of LEDs, which may be sixteen in number. The tight cluster enables the off-center positioning of the light source as noted above. The tight LED array generates considerable heat, making the LED mounting board and surrounding areas hotter than would be the case if the LEDs were spread around the entire face of the housing. To dissipate the heat the LEDs are mounted onto a metal core board, and the face of the unit preferably is mostly metal and contacts the LED board. This provides an efficient heat sink for the LED array. Only a small sealed window is provided, directly in front of the LED cluster.
Federal Aviation Administration (FAA) regulations require that devices generating significant amounts of heat must have the power source and heat generating element physically disconnected for air travel. So the device must allow a user easily to physically disconnect the LED cluster from the battery at some point in the circuit. Most dive lights do this by either (a) allowing the user to disconnect and/or remove an internal battery, or (b) using a separate battery housing with a cable and connector leading to the light head. The former requires opening a part of the device that is typically sensitive to water intrusion. Opening and closing a pressure seal repeatedly can and does introduce physical damage or dirt and grime to the seal, providing a path to potential flooding and corrosion. The latter adds a second pressure hull and a flexible cable, both of which are additional potential failure points.
An important second aspect and form of the invention therefore encompasses an advanced sealing setup. In use it is an entirely self-contained assembly, but it allows disconnection for FAA compliance, and when disconnected the separate assemblies are themselves completely sealed. Specifically, in this form the face plate assembly containing the LEDs is an individual pressure hull, but it can be easily removed by unthreading the bezel ring and pulling the face plate assembly off of the body unit. The body unit is itself an individual pressure hull. As an added benefit for easy storage and to prevent possible damage, the bezel ring allows the face plate assembly to be flipped over and stored backward, so that the device is electrically disconnected but physically in one piece.
In order to allow this easy disconnect, the back of the metal core circuit board is equipped with a series of exposed contact pads on the rear face. These pads are plated with a corrosion-resistant material, typically gold, and they are contacted by a series of spring-loaded knee-type contacts attached to an intermediary plate on the front of the body unit. The knee-type contacts are also plated with corrosion-resistant material. A heavy-gauge nonconductive alignment pin is used to help the user align the face plate assembly to the body unit so the connections are made reliably. The face plate assembly is sealed to the body unit by a large bore o-ring so that the entire area between the face plate assembly and the body unit is dry.
Another important part of the face plate assembly and body unit structure is cooling of electronics contained in the body unit. While the LEDs produce most of the heat in the system, the drive electronics can produce upwards of 10%, or about 6 watts when running at 4000 lumens. Without proper heat dissipation the drive electronics can overheat and fail. For this reason, in this second form of the invention, the intermediary plate is equipped with thermal transfer pads that interface to wide areas on the rear of the face plate assembly, providing a relatively short thermal path from hot components to intermediary plate to face plate to water. In this form, both the metal core circuit board and the intermediary plate are passing heat through the face plate to the water, which is fairly efficient.
In order to output the maximum amount of light possible, LEDs must be cooled as much as possible. In a typical case, cooling the LEDs from 55 down to 45 degrees Celsius will increase output approximately 100 lumens when running at 4000 lumens, with no other changes, so the shortest heat path from LED to water is desirable.
In the first and second forms of the invention, the metal core circuit board is connected around its edges to the face plate. Thus all the heat must travel laterally across the metal core circuit board to be conducted away. In a third form of the invention, the face plate assembly is not sealed to the body unit, but instead it has large holes to allow water flow into the cavity between body unit and face plate assembly. The face plate assembly has a large rear cap that encloses the metal core circuit board to protect it from corrosion. This rear cap also has a collared area that extends toward the intermediary plate and creates a sealed volume around the connector pads and connector. Thus the heat path is through the thickness of the metal core circuit board and the thickness of the rear cap, rather than along a greater lateral distance.
In a fourth form of the invention, the metal core circuit board is allowed to directly contact the water, for even better cooling. This can introduce corrosion on the metal core circuit board, but if the device is properly rinsed in fresh water and dried between uses (typical and customary for this type of equipment) the corrosion is minimal and the heat path is reduced further to just metal core circuit board to water. In this form, the rear cap takes a different form and is just the collar bolted to the central area of the metal core circuit board, to form the sealed volume around the connector. Additional benefits of this form are reduction in overall weight, and increased volume of cooling water inside the head, due to the smaller sealing collar instead of the fully enclosing cap of the third form.
Another form of the invention that is compatible with any of the four sealing and thermal solutions discussed above, employs a second array of LEDs added to a larger metal core circuit board. The multi-function switch on the body unit provides the user the ability to easily turn on one or the other array of LEDs. The second array can be a different color such as red, can be electromagnetic energy outside the visible spectrum such as infrared or UV light, or can be any wavelengths of light focused by dedicated optics, such that the upper array can provide a wide flood light and the lower array a focused spot beam. The advantage of the clustered arrays is that the blue or red filters held by the rotating filter ring enable use of light either filtered or unfiltered, by rotating the filter ring into various positions.
Another benefit of the removable front plate is the ability to provide interchangeable face plate assemblies to a user. A user might choose to switch face plates (a) to upgrade to a new brighter set of LEDs, (b) to replace a failed face plate or body unit, (c) to switch between colors or types of single-mode face plate units, for instance spot-only for flood-only, (d) to switch from a single-mode face plate unit to a multi-mode face plate unit such as spot plus flood. The body unit electronics can be designed to recognize the available use modes of the attached face plate unit by a detector circuit, and adjust the type of switching available to increase ease of use.
A typical equipment setup for underwater still photography includes a sealed camera housing and one or more underwater strobe units. In the past, film photography required the intense output of powerful flashbulbs; these flashbulbs produced very short bursts of light typically 8-10 times as bright as video lights. Digital photography increasingly allows use of much less powerful lighting to achieve the same results. As self-contained underwater lights increase in power, it is possible to completely replace dedicated flash units with video lights in some situations. Replacing strobes is even more practical if the video lights are capable of producing short bursts at increased power levels, for instance two times the maximum constant output of the light for video use. The final form of the invention, which is compatible with all other forms previously discussed, addresses this need. In this form, one or more large capacitors are added to the electronic circuit to provide a short, powerful burst of energy, which along with the power available directly from the battery, is capable of generating the flash output. The battery charges the capacitor(s) in between flashes. The flash is timed to the shutter of the camera by a synch cable. The synch cable can be a fiber optic cable carrying light from the camera's flash unit, or an electronic cable carrying an industry-standard synch signal.
The light unit of the invention is charged using external wet style connectors, allowing the unit to be sealed at the factory and never opened in the field, improving reliability for the diver.
It is an object of the invention to improve over previous dive lights available for video support, including in brightness, duration, cooling efficiency, and convenient filtering of the light beam as needed. These and other objects, advantages and features of the invention will be apparent from the following description of a preferred embodiment, considered along with the accompanying drawings.